The technology described here generally relates to fusion bonding using dynamic frictional energy and, more particularly, friction welding by rotating one work surface relative to another about an axis.
Friction welding is a process in which metals, and/or other materials, are joined by heat which is generated when the parts are rubbed together under high pressure. The advantages of friction welding include very rapid completion rates, good mechanical properties, and the elimination of the need for shielding gases under most circumstances. There are at least twenty variants of friction welding processes. Some of those variants include rotary friction welding, friction stud welding, radial friction welding, linear friction welding, orbital friction welding, third-body friction welding, and friction taper plug welding.
Friction stir welding is a relatively new friction welding process. It involves rotating a small tool between two closely-butted components. Frictional heating causes the materials in the components to soften and the forward motion of the tool forces material from the front of the tool to the back, where it consolidates to form a solid state weld. Stir welding processes thus combine the flexibility of mechanized arc welding with the desirable results of friction welding.
Friction stir welding has been used to join various materials that will soften and co-mingle under applied frictional heat, including as metals and plastics. For example, U.S. Pat. No. 5,975,406, filed Feb. 27, 1998 by Mahoney et al. (and assigned at issuance to the Boeing Company) discloses a method to repair voids in aluminum alloys, and is incorporated by reference here in its entirety. As reproduced in FIG. 1 of the present application, an aluminum work piece 30 with an anomaly void is machined in order to provide a tapered bore 34 with grooves and ridges 36 provided on the surface of the bore. A consumable tapered plug 38 is then inserted into the tapered bore 34 with a larger section 40 connected to a rotating motor (not shown).
As shown in FIG. 2, the included angle cc of the tapered bore 34 is preferably greater than the included angle of the tapered plug 38 in order to ease rotation of the tapered plug, and to prevent air from being between the tapered plug, tapered bore, and/or tapered ridges 36. Until now, however, the shapes of the tapered plug 38 and tapered bore 34 have not been adequately considered with regard to friction stir welding and/or other friction welding processes.
These and other drawbacks of conventional technology are addressed here by providing a joining method and friction welded structure including a first member with a conoid recess, and a second member with a second conoid tip that is friction welded to the recess in the first member. One, or both, of the conoids is preferably a non-spheroid, such as a paraboloid. In addition, the conoid recess preferably has a vertex angle that is greater than the vertex angle of the conoid tip.